Microwave stripling circuits with selectively bondable micro-sized switches for in-situ tuning and impedance matching

ABSTRACT

A microstrip line is divided into a number of short sections, each capacitively coupled to its neighbor by a cantilever switch. The coupling of each switch depends on the separation between sections and the spacing between the catilever switch and an adjoining section. The cantilever switches are sufficiently flexible to allow test contact between adjacent sections and is permanently bondable where desired. In such a manner sections having lengths chosen to be predetermined fractions of a desired wavelength are connected together to shift the phase of energy propagating therealong to provide tuning and impedance matching of microstrip circuits.

Unite States Patent [191 Heng et al. Mar. 12, 1974 [54] MICROWAVESTRIPLING CIRCUITS WITH 2,814,022 11/1957 Furlow, Jr. et al.., 333/234 MSELECTIVELY BONDABLE MICROSIZED 2,819,452 l/1958 Arditi et a1. 333/73 SSWITCHES FOR INSITU TUNING AND 3,582,833 6/1971 Kordos 333/84 IMPEDANCEMATCHING FOREIGN PATENTS OR APPLICATIONS 75 Inventors; Terrence M Hang;Harvey 0 159,667 11/1954 Australia 333/84 M Nathanson; John R. Davis,Jr., all of Pittsburgh, Pa.

Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: July 16, 1971 Appl. No.2 163,367

US. Cl 333/84 M, 333/7, 333/73 S,

333/81 A [51] Int. Cl. H01p 3/00, HOlp 3/08 [58] Field of Search 333/11,73 S, 81 A, 84 M, 333/7 [5 6] References Cited UNITED STATES PATENTS2,859,417 11/1958 Arditi .l 333/84 M 2,751,558 6/1956 Grieg et al 333/73S 3,413,573 11/1968 Nathanson et al. 332/31 T 2,773,242 12/1956 Grieg333/97 S Primary Examiner-Rudolph V. Rolinec Assistant Examiner-SaxfieldChatmon, Jr. Attorney, Agent, or Firm-D. Schron 5 7] ABSTRACT minedfractions of a desired wavelength are connected together to shift thephase of energy propagating therealong to provide tuning and impedancematching of microstrip circuits.

11 Claims, 10 Drawing Figures rah/965L976 PATENTEU MAR 12 I974 SHEET 1BF 3 WITNESSES INVENTORS Terrence M.S. Heng ,Harvey C. Nothonson andJohn R. Davis Jr. BY

DEM/L, VLOIA ATTORNEY BACKGROUND OF THE INVENTION 1. Field of theInvention A The present invention relates generally to microstrip vcircuits and more particularly relates to microwave striplines capableof in-situ tuning.

2. Description of the Prior Art The lack of an efficient and reliablemeans for tuning has always been a major problem in microwave integratedcircuit technology. For passive circuits this problem has beeneliminated to some degree by imposing a high degree of tolerance andfabrication, usually at an increased cost. The situation becomes evenmore serious, however, for active circuits, in both monolithic andhybrid configurationsln the former case, the effective impedance of theactive device is generally different from theoretical design and theneed for matching is evident. The common practice in hybrid circuits isto characterize the active device prior to insertion of the device intothe circuit. In this way the range of device parameters can beaccommodated by sequence of circuit designs. This involves theavailability of costly high quality, sophisticated test equipment andcomputer facilities, and a full understanding of devicecircuitinteraction. In short, the approach is not economically feasible forsmall production runs.

At present, a limited number of tuning techniques exist which fall intotwo broad categories: (i) active tuning, and (ii) mechanical tuning. Theuse of varactor and pi-n diodes as tunable capacitive elements, and YIGspheres as tunable inductive elements, fall into the first category.Mechanical tuning by screw and movable magnetic slugs have also beenused, in addition to the simple technique of line scraping by laser orother means. With the exception of the latter, all these techniquesinvolve the introduction of an external element into the circuit. Assuch, the electrical and mechanical stabilities of these elements are ofconcern in a large number of applications.

CROSS REFERENCE TO RELATED APPLICATIONS AND PATENTS U.S. Pat. No.3,539,705, entitled Microelectronic Conductor Configuration and Methodof Making the Same by Harvey C. Nathanson and John R. Davis, andassigned to the present assignee, discloses and claims a microelectronicconductor configuration wherein two conductive layers are spaced apart,the second layer including a plurality of projecting paths that can beselectively, permanently bonded to the first layer to effect electricalconnection therewith.

In patent application Ser. No. 40,627 which is a divisional applicationof the aforementioned patent the method of forming such configurationsis described and claimed.

In U.S. Pat. No. 3,413,573 issued Nov. 26, 1968, entitledMicroelectronic Frequency Selective Apparatus with Vibratory Member andMeans Responsive Thereto by Harvey C. Nathanson and Robert A. Wickstrom,and assigned to the present assignee, there is described and claimedstructures and methods of making such structures involving spaced metalmembers on integrated circuits, such as for cantilever beams andresonant gate transistors and for conductive crossovers.

SUMMARY OF THE INVENTION Briefly, the present invention allows in-situtuning and impedance matching of microstrip circuits by providing amicrowave stripline of a length related to the wavelength of the desiredoperating frequency, which stripline is divided into' a plurality ofsections, each of a length chosen to be a selected fraction of thewavelength. A plurality of cantilever switches of material similar tothe sections are positioned to interconnect sections. Each cantileverswitch has a first portion affixed to its associated section and asecond portion extending over but spaced from an adjacent section. Theover extending portion can be selectively permanently bonded to theadjacent section. The cantilevers are selected to be sufficientlyflexible to allow temporary electrical contact to be made for tuning andimpedance matching. The number-of sections so connected togetherdetermines the amount of phase shift imparted to energy propagatingalong the stripline.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding-of theinvention, reference may be had to the preferred embodiment, exemplaryof the invention, shown in the accompanying drawings, in which:

FIG. 1 is a perspective view of a cantilever switch utilized in theinventive embodiment;

FIG. 2 is an elevational view of such a cantilever switch;

FIG. 3 is a diagrammatic illustration of an illustrative embodiment ofthe present invention;

FIG. 4 is a graphical illustration of the performance of theillustrative embodiment shown in FIG. 3;

FIGS. 5 through 8 are partial sectional views of a structure atsuccessive stages in fabrication in accordance with the presentinvention;

FIG. 9 is a plan view of microwave circuitry embodying the presentinvention; and

FIG. 10 is a plan view of an alternate embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION Simple in-situ trimming of amicrowave strip is accomplished by dividing the line into a number ofshort sections, each capacitively coupled to its neighbor by acantilever switch as shown in FIG. 1. Sections 2 and 4 are spaced aparta certain distance l A cantilever switch 6 has a first part 8 secured tosection 2 and a second portion 10 extending over but spaced from theadjacent section 4. The part 10 is based a distance I from the section4; The coupling of each switch depends on the dimensions 1,, and 1, fora given line and substrate, and can be approximated by C3 z C CD d 60 W6 u)/ d where:

C; and C, are capacitances illustrated in FIG. 2 s is permittivity offree space and C, is approximately equal to o z w (n) where K(m) is acomplete elliptical integral of the first kind of modulus m. The modulusconstants m and n are m (b a /b and n 5 all; (4)

where:

h thickness on dielectric substrate ed dielectric constant of substrateq Wheeler filling factor.

For a 0.020 inch wide microstrip line of a 0.020 inch substrate having adielectric constant of 8.875 such as sapphire for example, thecalculated value of C is 0.0146 pf, which agrees very closely with themeasured results set forth in Microwave Engineers Handbook and BuyersGuide, Horizon House inc. 1967 by H. Stinehelfer.

For a switch of dimensions: I 0.004 inch, 1, 0.0002 inch, a width W of0.002 inch, .a length 1, of 0.007 inch and a dielectric constant e d 10,the theoretical capacitance is of the order of 0.9 lfarads,corresponding to a reactance of 2.94 kilohms at 6 GHZ or a reflectioncoefficient of 0.945. The measured value was 0.9. The lower measuredvalue is due to the fringing fields at the gap which have been ignoredin the calculation, and finite losses of the line and connectorsections. A low capacitance can be obtained by increasing the switchheight L and gap separation 1,, and decreasing the cantilever length fora given line.

To investigate the loss and reflection properties of a number of suchswitches, a simple circuit was constructed as shown in FIG. 3. Thecenter line section 20 consisted of an 85 ohm (0.002 inch).line of onewavelength at 6 Gl-lz, which was divided into 5/8 sectionsinterconnected by seven switches. Matching at both ends of the .line to50 ohm miniature connectors was achieved by quarter-wave (65 ohm)transformers 22. The relative phase-shift introduced by the closing ofeach switch is shown in FIG; 4. When all the switches were closed, theinput voltage standing wave ratio was measured to be 1.4 and theinsertion loss was 1.9 db at 6 Gl-iz, of which at least 1.2 db isattributed to line and connector losses at this frequency. The averageloss is therefore less than 0.1 db per switch for the dimensions givenwhich are by no means optimized.

More particularly, referring to FIG. 4 it can be seen that as eachswitch is closed the energy propagating along the line is shifted inphase the desired 45. Of course, the stripline may be divided into aplurality of sections of any chosen number to provide incremental phaseshift and impedance matchings as may be desired.

When the switches are fabricated of gold, bonding is readily achievedwith a wedge bonder at room temperature. The cantilever switches aresufficiently flexible to allow temporary contact between sectionswithout permanently bonding by the application of a slight pressure withthe bonder. On removal of this pressure, the cantilever springs back toits original position without deterioration of electricalcharacteristics. Thus, it is possible to effect atest contact withoutbonding to determine optimum matching. Calculations have also been madeto determine the stability of the switches under external stress.Suffice it to say, for the dimensions stated, an external accelerationof 20,000 Gs would be required to cause contact to be made by acantilever switch 'to an adjacent section.

A further understanding of the invention on the flexibility with whichit may be used will be aided by consideration of the followingdescription of preferred methods for carrying out the present invention.FIGS. 5 through 8 show steps in the fabrication process. In FIG. 5 afirst continuous interfacial bonding material 30 is deposited upon asuitable substrate 32 such as sap-' phire, alumina, quartz to name afew. The interfacial bonding material 30 may be a metallization layersuch as titanium 30a and gold 306. A pattern of sections 34 of anothermetal layer is deposited upon the layer 30 to define the switch gapswith the rest of the circuitry.

In FIG. 6 spacing material 36 is then placed in the gaps and onto aportion of each section 34. This is followed by the plating of metalcantilevers 3 as shown in FIG. 7. Sections 34 andcantilevers 38 may beof a metal selected from the group consisting of nickel, copper, silver,cadmium, gold, tin, palladium, aluminum and nickel-iron alloys.

The spacers and excess metalization are then removed by successiveetching to form the switches as illustrated in FIG. 8. Because the stepsinvolved are the same for one or a number of switches, batch fabricationis therefore possible. For a total switch length L, a lower limit on theseparation between adjacent switches would probably be twice thatlength. Using the 0.010 inch switches fabricated above, line lengthtrimming in steps 0.020 inch, or 8.6 for an 85 ohm line at 6 GHz, ispossible. The resolution could be improved further with smaller switchesof lengths say one-half of those previously stated.

The present invention has application in tuning and impedance matchingof microstrip circuits. For example, in FIG. 9, strip lines 40, 42 and44 may be lengthened for desired tuning of the microstrip IMPATToscillator circuit by closing selected cantilever switches. Moreparticularly, the solid state IMPATT diode is mounted in position 46 ona heat sink and dc. is brought in by the bias pad 48. Connection to thediode is made by wire bonding from pad 48. Tuning of the IMPATT diode isachieved by varying lines'42 and 44, and impedance matching of theoscillator to load line 50 is provided by line 40.

An alternate embodiment of the present invention is as illustrated inFIG. 10. As shown therein, a center line conductor 52 may be increasedin width by the addition of adjacent lying conductors 54, 56, 58 and 60.By simply permanently bonding the cantilever switch 62 disandmodifications within the spirit and scope of the It will, therefore, beapparent that there has been disclosed a reliable method of tuningmicrowave integrated circuit line connection which has a potential up tothe expand. The advantages of this concept are: (1) high open circuitimpedance, VSWR greater than 20, (2) low short-circuit insertionloss,'le ss than 0.1 db, (3)

high trim resolution, approximately 8 or lower at 6GHZ, (4) low lineperturbations, (5) high stability under mechanical stress, and (6)in-situ fabrication with the rest of the microwave integrated circuitry.

We claim as our invention:

1. A stripline conductor for tuning and impedance matching of microwavecircuitry comprising, in combination; a plurality of line sections, eachof a length chosen to be a selected fraction of a wavelength; aplurality of cantilever switches each associated with their respectiveone of said sections and having a first portion affixed thereto and asecond section extending over but spaced from an adjacent section butwhich second section can be selectively permanently bonded to saidadjacent section whereby the phase shift along said stripline is afunction of the number of switches which are bonded closed.

2. A microwave stripline of substantially one wavelength at the desiredfrequency of operation comprising, in combination; a plurality ofsections, each of a length chosen to be a selected fraction of saidwavelength; a plurality of cantilever switches each associated with arespective one of said sections and capacitively coupling said one ofsaid sections to an adjacent section; each said cantilever switch havinga first portion affixed to said one of said sections and a secondportion extending over but spaced from its adjacent section; thecapacitive coupling between sectionsbeing related to the separationbetween adjacent sections and the space between the overhanging secondportion and said associated adjacent section as well as the extent towhich said second section extends over said associated adjacent section;said plurality of cantilever switches being sufficiently flexible toeffect a test contact between adjacent portions upon application ofslight pressure thereupon; each of said plurality of cantilever swithcesbeing selectively, permanently bondable to its associated adjacentsection whereby the capacitative coupling between adjacent sections iselectrically shorted and the energy propagating along said stripline isshifted in phase in accordance with the number of sections so connectedto accomplish tuning and impedance matching.

3. The subject matter of claim 2 including impedance matching means ateach end of said stripline.

4. The subject matter of claim 3 wherein said impedance matching meansincludes quarter-wave transformers.

5. The subject matter of claim 2 wherein the neighboring sections are atleast twice the length of their associated cantilever switch length.

6. A microelectronic component comprising, in combination; a substrate;a first pattern of conductors on a surface of said substrate; aplurality of cantilever switches each associated with a respective oneof said conductors and having a first portion affixed thereto and asecond portion extending over but spaced from an adjacent conductor;each of said cantilever switches being sufficiently flexible to effect atest contact between adjacent conductors; each of said flexible switchesbeing selectively, permanently bondable to its associated adjacentconductor to widen the current path whereby adjacent conductors areselectively connected in parallel circuit relationship whereby the'width of the resultant electrical path is increased.

7. A method of making a microwave stripline with selectively cold-flowbondable micro-sized switches for in-situ tuning on a substratecomprising the steps of; depositing a first continuous metal layer on asurface of said substrate; depositing a pattern of conductive sectionsof a second metal layer on said first layer to define switch gapsbetween said sections; depositing a layer of spacing material in thegaps between said sections and onto a portion of each said section;depositing a third metal layer over a portion of each said section and apart of said spacing material to an extent that the third metal layeroverlaps a part of said second metal layer; removing the spacers andexcess metalizations by successive etchings to form the cantileverswitches.

8. The method of claim 7 wherein; said substrate is a member selectedfrom the group consisting of sapphire, alumina and quartz.

9. The method of claim 8 wherein the second and third layers are ofgold.

10. The method of claim 9 wherein said second and third metals are themembers selected from the group consisting of nickel, copper, silver,cadmium, gold, tin, palladium, aluminum and nickel-iron alloys.

11. A microwave stripline switch arrangement for use at an operatingwavelength, comprising: a first stripline section, at least a secondstripline section spaced from said first section, a cantilever switchsection connected to said first stripline section and extending over andspaced from said second stripline section and connectable therewith,said sections being of a combined length to effect phase shifting ofmicrowave energy of said wavelength when contact is effected betweensaid cantilever switch section and said second stripline section.

1. A stripline conductor for tuning and impedance matching of microwavecircuitry comprising, in combination; a plurality of line sections, eachof a length chosen to be a selected fraction of a wavelength; aplurality of cantilever switches each associated with their respectiveone of said sections and Having a first portion affixed thereto and asecond section extending over but spaced from an adjacent section butwhich second section can be selectively permanently bonded to saidadjacent section whereby the phase shift along said stripline is afunction of the number of switches which are bonded closed.
 2. Amicrowave stripline of substantially one wavelength at the desiredfrequency of operation comprising, in combination; a plurality ofsections, each of a length chosen to be a selected fraction of saidwavelength; a plurality of cantilever switches each associated with arespective one of said sections and capacitively coupling said one ofsaid sections to an adjacent section; each said cantilever switch havinga first portion affixed to said one of said sections and a secondportion extending over but spaced from its adjacent section; thecapacitive coupling between sections being related to the separationbetween adjacent sections and the space between the overhanging secondportion and said associated adjacent section as well as the extent towhich said second section extends over said associated adjacent section;said plurality of cantilever switches being sufficiently flexible toeffect a test contact between adjacent portions upon application ofslight pressure thereupon; each of said plurality of cantilever swithcesbeing selectively, permanently bondable to its associated adjacentsection whereby the capacitative coupling between adjacent sections iselectrically shorted and the energy propagating along said stripline isshifted in phase in accordance with the number of sections so connectedto accomplish tuning and impedance matching.
 3. The subject matter ofclaim 2 including impedance matching means at each end of saidstripline.
 4. The subject matter of claim 3 wherein said impedancematching means includes quarter-wave transformers.
 5. The subject matterof claim 2 wherein the neighboring sections are at least twice thelength of their associated cantilever switch length.
 6. Amicroelectronic component comprising, in combination; a substrate; afirst pattern of conductors on a surface of said substrate; a pluralityof cantilever switches each associated with a respective one of saidconductors and having a first portion affixed thereto and a secondportion extending over but spaced from an adjacent conductor; each ofsaid cantilever switches being sufficiently flexible to effect a testcontact between adjacent conductors; each of said flexible switchesbeing selectively, permanently bondable to its associated adjacentconductor to widen the current path whereby adjacent conductors areselectively connected in parallel circuit relationship whereby the widthof the resultant electrical path is increased.
 7. A method of making amicrowave stripline with selectively cold-flow bondable micro-sizedswitches for in-situ tuning on a substrate comprising the steps of;depositing a first continuous metal layer on a surface of saidsubstrate; depositing a pattern of conductive sections of a second metallayer on said first layer to define switch gaps between said sections;depositing a layer of spacing material in the gaps between said sectionsand onto a portion of each said section; depositing a third metal layerover a portion of each said section and a part of said spacing materialto an extent that the third metal layer overlaps a part of said secondmetal layer; removing the spacers and excess metalizations by successiveetchings to form the cantilever switches.
 8. The method of claim 7wherein; said substrate is a member selected from the group consistingof sapphire, alumina and quartz.
 9. The method of claim 8 wherein thesecond and third layers are of gold.
 10. The method of claim 9 whereinsaid second and third metals are the members selected from the groupconsisting of nickel, copper, silver, cadmium, gold, tin, palladium,aluminum and nickel-iron alloys.
 11. A microwave stripline switcharrangement for use at an operating wavelenGth, comprising: a firststripline section, at least a second stripline section spaced from saidfirst section, a cantilever switch section connected to said firststripline section and extending over and spaced from said secondstripline section and connectable therewith, said sections being of acombined length to effect phase shifting of microwave energy of saidwavelength when contact is effected between said cantilever switchsection and said second stripline section.